10How to Incorporate JavaScript into an Application

Adding JavaScript to a Web application is a great way to add features that mimic those found in client/server applications without sacrificing all of the benefits of Web deployment. Oracle Application Express includes multiple built-in interfaces especially designed for adding JavaScript.

Remember that JavaScript is not appropriate for data intensive validations. For example, to verify that a name is contained within a large database table, you would need to pull down every record to the client, creating a huge HTML document. In general, complex operations are much better suited for server-side Oracle Application Express validations instead of JavaScript.

This tutorial describes some usage scenarios for JavaScript and includes details about how to implement them in your application.

Incorporating JavaScript in the HTML Header Attribute

One way to include JavaScript into your application is to add it to the HTML Header attribute of the page. This is a good approach for functions that are specific to a page as well as a convenient way to test a function before you include it in a.js file.

You can add JavaScript functions to a page by entering the code in the HTML Header attribute on the Page Attributes page.

To add JavaScript code in the HTML Header attribute:

On the Workspace home page, click the Application Builder icon.

Select an application.

The Application home page appears, displaying its set of pages.

Click a page.

The Page Definition for that page appears.

In the Page section, click the Edit page attributes icon.

The Edit Page appears.

Scroll down to the HTML Header section.

Enter code into HTML Header and then click Apply Changes.

For example, adding the following code would test a function accessible from anywhere on the current page.

Including JavaScript in a .js File Referenced by the Page Template

In Oracle Application Express you can reference a.js file in the page template. This approach makes all the JavaScript in that file accessible to the application. This is the most efficient approach because a.js file loads on the first page view of your application, and is then cached by the browser.

The following code demonstrates how to include a .js file in the header section of a page template. Note the line script src= that appears in bold.

About Referencing Items Using JavaScript

When you reference an item, the best approach is to reference the item name as it is defined within the page. Note that item name is different than the item label. The item name displays on the Page Definition and the label displays on a running page. For example, if you create an item with the name P1_FIRST_NAME and a label of First Name, you would reference the item using P1_FIRST_NAME.

Referencing an item by the item name enables you to use the JavaScript method getElementById() to get and set item attributes and values. The following example demonstrates how to reference an item by ID and display its value in an alert box.

<script type="text/javascript">
function firstName(){
window.alert('First Name is ' + document.getElementById('P1_FIRST_NAME').value );
}
// or a more generic version would be
function displayValue(id){
alert('The Value is ' + document.getElementById(id).value );
}
</script>
// Then add the following to the "Form Element Attributes" Attribute of the item:
onchange="displayValue('P1_FIRST_NAME');"

Calling JavaScript from a Button

Calling a JavaScript from a button is a great way to confirm a request. Oracle Application Express uses this technique for the delete operation of most objects. For example, when you delete a button, a JavaScript message appears asking you to confirm your request. Consider the following example:

This example creates a function to confirm a delete action and then calls that function from a button. Note that the function optionally submits the page and sets the value of the internal variable :REQUEST to Delete, thus performing the delete using a process that conditionally executes based on the value of request.

Note that when you create the button, you need to select Action Redirect to URL without submitting page. Then, you specify a URL target, such as the following:

confirmDelete('Would you like to perform this delete action?');

Changing the Value of Form Elements

In the following example, there are four text boxes in a region. The fourth text box contains the sum of the other three. To calculate this sum, you add a JavaScript function to the HTML Header attribute and then call that function from the first three items.

Creating a Client Side JavaScript Validation

Client side validations give immediate feedback to users using a form. One very common JavaScript validation is field not null. This type of validation works well in the page header rather than in a.js because it is so specific to a page.

Before you begin, you need to import and install the OEHR Sample Objects application in order to access the necessary sample database objects. See "About Loading Sample Objects".

Enabling and Disabling Form Elements

While Oracle Application Express enables you to conditionally display a page item, it is important to note that a page must be submitted for any changes on the page to be evaluated. The following example demonstrates how to use JavaScript to disable a form element based on the value of another form element.

First, you write a function and place it in the HTML Header attribute of the page containing your update form. Second, you call the function from an item on the page. The following example demonstrates how to add a JavaScript function to prevent users from adding commissions to employees who are not in the Sales Department (P2_DEPARTMENT_ID = 80).

Create a Call to the disFormItems Function

Finally, you need to create a call to the disFormItems function after the page is rendered to disable P2_COMMISSION_PCT if the selected employee is not a Sales representative. A good place to make this call would be from the Page HTML Body Attribute.

To create a call to the disFormItems function:

Go to the Page Definition for page 2.

Under Page, click the Edit page attributes icon.

The Edit Page appears.

Locate the Display Attributes section.

From Cursor Focus, select Do not focus cursor.

Selecting Do not focus cursor prevents conflicts between generated JavaScript and custom JavaScript.

Scroll down to the HTML Body Attribute section.

In the Page HTML Body Attribute, enter the following:

onload="disFormItems(); first_field();"

Click Apply Changes.

Run the page.

Figure 10-5 demonstrates the completed form. Note that Department ID displays as a select list. Also notice that the Commission Pct field is unavailable since the Department ID is Administration.